sam build files on xgboost-inference-arm64-docker-lambda

clean build fails as shown below -- basically blocks ability to develop/deploy arm64/graviton functions

```
Status: Downloaded newer image for public.ecr.aws/lambda/python:3.8-arm64 ---> f7892dec0f19
Step 2/7 : COPY requirements.txt ./
---> f326d820d212
Step 3/7 : RUN python3.8 -m pip install -r requirements.txt -t .
---> [Warning] The requested image's platform (linux/arm64/v8) does not match the detected host platform (linux/amd64/v3) and no specific platform was requested
---> Running in 18c403fbd949
exec /bin/sh: exec format error

Build Failed
Error: XGBoostInferenceArm64Function failed to build: The command '/bin/sh -c python3.8 -m pip install -r requirements.txt -t .' returned a non-zero code: 1
```

system info:

```
$ uname -a
Linux ### 5.19.0-42-generic #43~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Fri Apr 21 16:51:08 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
```